1. Field of the Invention
The present invention relates to a wet etching system for manufacturing semiconductor devices and a wet etching method using the same, and more particularly, to a wet etching system and method for etching a nitride layer, formed on a semiconductor substrate, for a short period of time while maintaining the concentration of phosphoric acid (H3PO4) constant.
2. Description of the Related Art
Generally, semiconductor devices are manufactured by forming multiple insulating layers or conductive layers on a semiconductor substrate, and then forming a specific electrical pattern on the layers according to desired characteristics of the particular semiconductor device being manufactured.
The formation of the specific pattern is achieved by selectively removing designated portions of the insulating layers and/or the conductive layers by an etching process. There are two types of etching processes: dry etching using a plasma generated in a reaction chamber, and wet etching using a particular chemical that is capable of removing the layer to be etched. The wet etching process is carried out using a wet etching system employing a tank containing the chemical etchant.
FIG. 1 schematically illustrates a conventional etching system for manufacturing semiconductor devices, employing a chemical bath comprising a tank 10 for containing a chemical 16 for etching a certain layer on the semiconductor substrate. Normally, the chemical 16 is diluted with deionized water, with the degree of dilution being controlled depending on the etching process.
A heater 12 heats the chemical 16 inside the tank 10 to a certain temperature sufficient for the process conditions of the etching process. Typically, bar-shaped heaters 12 are disposed in the chemical 16 at opposing sides of the tank 10.
A bubbler 14 is connected to the tank 10 and is used to generate bubbles in the chemical 16 inside the tank 10 in order to improve the reaction of the chemical 16 and a wafer placed in the chemical bath.
The temperature of the chemical 16 and the etching process time are important parameters in the etching process. However, heating the chemical 16 causes the deionized water, which was used to dilute the chemical, to evaporate. As a result, the concentration of the chemical 16 within the tank 10 is increased due to the evaporation of the deionized water, and thus, deionized water must be supplied in an amount equal to the evaporated amount in order to maintain the chemical 16 concentration constant. In some cases, additional amounts of chemical 16 are supplied to the tank 10 to maintain the chemical 16 concentration constant.
However, precisely controlling the concentration changes of the chemical due to the evaporation of the deionized water is not easy, despite the continuous supply of the deionized water, because the concentration of the chemical 16 inside a the tank 10 is not constant.
Although the chemical concentration changes can be detected by changes in the etch rate observed during the etching process, such observations occur after a particular wafer may have suffered a fatal defect caused by a failure of the pattern profile during the etching process. In other words, precise control of the etching process is difficult when using data generated after the etching process is performed.
Another drawback of the conventional wet etching system is that the temperature of the chemical 16 decreases as the deionized water is continuously supplied to the tank 10, and thus the heater 12 must be continuously driven to heat the chemical 16 to the desired etching temperature, which shortens the life span of the etching system itself.
Referring to FIG. 1, the etching process for a nitride layer is described. First, a chemical 16 for etching the nitride layer, such as phosphoric acid (H3PO4), is supplied in the tank 10. The concentration of the phosphoric acid (H3PO4) is 85%, with the remainder being deionized water. Although the phosphoric acid concentration is relatively high, the etch rate for the nitride layer is good at this concentration value.
The phosphoric acid (H3PO4) is heated so as to maintain its temperature between about 170xc2x0 C. to 174xc2x0 C. according to the process conditions of the etching process, and then, the etching process is carried out. The etching process time depends on the thickness of the nitride layer.
However, as describe above, the required continuous supply of deionized water and the chemical to the tank 10 causes difficulties in trying to precisely control the chemical concentration inside the tank 10; which causes uneven etch rates. Further, because the heater 12 is bar-shaped, it takes a long time to heat the phosphoric acid (H3PO4) and maintain its temperature, which may damage the heater and shorten the life time of the etching system.
Moreover, after the etching process is completed, the disposal and the cleaning of the remaining waste solution, including the deionized water, the chemical, etc. due to the continuous supply thereof remains a difficult problem.
The present invention is directed to a wet etching system for manufacturing semiconductor devices and a wet etching method using the same, which provides efficient and precise execution of the etching process while maintaining the concentration of the chemical etchant constant.
Another object of the present invention is to provide a wet etching system for manufacturing semiconductor devices and a wet etching method using the same, which decreases the process temperature of the chemical to one that is lower than the conventional art, and increases the etch rate of the etching process, while maintaining the concentration of the chemical constant to thereby reduce the etching process time.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the wet etching system for manufacturing semiconductor devices comprises an open-topped tank containing a chemical diluted with deionized water to wet-etch a certain layer on a semiconductor substrate. A heater is disposed in the tank, and a cover is employed to cover the open top of the tank. The cover includes a cooling apparatus that condenses the deionized water evaporated by the heating of the heater.
The lower surface of the cover gradually slopes downwardly from opposing edges of the cover toward either a central lateral or longitudinal axis thereof, which facilitates collection of the condensed deionized water. A discharge opening is provided in the cover, in flow communication with the ambient outside of the tank, so that gas can be easily discharged from the tank.
The tank and the cover may be made of a chemically-resistant material, such as TEFLON(trademark), and the surface of the heater may be coated with TEFLON(trademark) as well.
In another aspect of the present invention, there is provided a wet etching method comprising supplying a chemical diluted with deionized water into a tank having a top portion with a cover arranged thereon, the cover having a cooling apparatus formed therein. A semiconductor substrate, having a layer thereon to be etched, is placed into the tank. A heater disposed within the tank maintains the chemical within a temperature range. The deionized water evaporates when the temperature range is greater than a boiling point of the deionized water. The deionized water then condenses on the cooler cover, before flowing back into the tank. The etching process is carried out while the evaporation and condensing steps are performed.
Where the layer to be etched is a nitride layer, the chemical supplied into the tank is a phosphoric acid (H3PO4) diluted with deionized water, the concentration of the phosphoric acid (H3PO4) being from 80% to 90%. The chemical is heated to maintain its temperature between about 153xc2x0 C. to 157xc2x0 C.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.